1. Field of the Invention
The present disclosure relates to a developing apparatus and a process cartridge.
2. Description of the Related Art
Image forming apparatuses such as electrophotographic copying machines, laser beam printers, and facsimiles are provided with a developing apparatus configured to develop an electrostatic latent image formed on a surface of a photosensitive member. The developing apparatus includes a toner container configured to store toner as a developer, a developing roller as a developer carrying member configured to carry and convey the toner, and a control blade configured to control the amount of toner on the developing roller constant (an amount-of-developer control blade) by being arranged in contact with the developing roller.
An excessive part of toner adhered to a surface of the developing roller from the toner container is removed when passing through a contact position with respect to the control blade in association with the rotation of the developing roller and is returned back to the toner container. At this time, the toner remaining on the developing roller moves to the surface of the photosensitive member by being provided with a friction charge (also referred to as “triboelectricity”) by a friction with respect to the control blade.
In the related art, as such a control blade, a configuration in which a blade member formed of a rubber-like resilient member is adhered to a metallic supporting member with an adhesive agent is known. In this configuration, the control blade is allowed to be brought into a press contact easily with the developing roller over the entire length with an even press-contact force, and high durability is achieved.
The surface of the blade member brought into press-contact with the developing roller has a function to control the friction charge of the toner, and hence is referred to also as a “charge control surface”. Examples of a material of the charge control surface include urethane rubber, a polyamide resin, a polyamide elastomer, silicone rubber, and a silicone resin.
In the developing apparatus compatible to high image quality and full-color image formation associated with speed enhancement, since toner having fine particles is used, a control blade which allows press-contact with the developing roller with higher uniformity is required.
Therefore, for example, Japanese Patent Laid-Open No. 2002-372858 discloses a control blade configured in such a manner that blade members having substantially the same shape, an adhesive agent, and a supporting member are laminated over the entire surfaces one on top of another to form layers. Japanese Patent Laid-Open No. 2008-90160 discloses a control blade configured in such a manner that a blade member covers an area of a supporting member over an area at least from a contact surface with respect to a developing roller to a distal end surface. By employing the control blade of this configuration, a uniform press-contact with the developing roller is enabled, and high image quality and full-color image formation may be accommodated.
In the control blades (control members) disclosed in Japanese Patent Laid-Open No. 2002-372858 and Japanese Patent Laid-Open No. 2008-90160, the blade members (covering members) adhered to and covered with the supporting member are kept in sliding contact with the developing roller while keeping a constant pressure. Therefore, the blade member is worn and shaved in association with the usage of the developing apparatus.
In particular, a pressure with respect to the developing roller is high at a portion of the blade member near longitudinal end portions or a portion sandwiched between an end seal for preventing toner leakage and the developing roller, and hence is susceptible to abrasion in comparison with an image forming area in the vicinity of a center of the control blade. In addition, the longitudinal end portions of the control blade may be positioned having an inflected shape, or may expose the adhered surface with respect to the supporting member. Consequently, when being shaved, separation may occur at a single stroke so as to be curled up from the longitudinal end portions and hence the supporting member may be exposed.
When such exposure of the supporting member caused by the wear or the separation as described above reaches the image forming area, the uniformity of the contact pressure cannot be maintained in the exposed portions and hence image defects such as formation of stripes or density unevenness may occur.